We have not tested the Voxmundi gw1600 with Diafaan SMS Server but if I look at the documentation of this device that I can find on the internet then I don't think it will work.

Diafaan SMS Server requires a modem (pool) that supports the GSM 07.05/07.07 AT command standard over a serial port or LAN connection or a wireless modem gateway that supports the SMPP standard. As far as I can determine, the Voxmundi gw1600 does not support one of these standards.